Chinese Invention Patent Application No.96120428.1 (corresponding to U.S. Application Serial No. 60/027,914) discloses a Fire-safe Halogen Torchiere Lamp with a grid in which a fuse or thermo-sensentive switch is functioned as a thermo-sentitive element. As shown in FIG. 1, a sensor 1 provided with such a sensing element is attacheded on a reflector 3. When a cover such as cheesecloth (in UL tests) or a white duck (in CSA tests) is put on a grid 2 at the lamp head and the tempeture is too high, the lamp switches off automatically to avoid any danger of fire. The lamp will switch on then automatically after the temperature is lowered. The cycle of lighting off to lighting up will continues and is apt to damage the life of the lamp and the cover before an additional manual operation stops the cycle.
FIG. 2 shows a halogen torchiere lamp, which is added a temperature control automatically protecting circuit having a locking function to overcome the above mentioned disadvanatge. As shown in the figure, when the temperature of the lamp L.sub.1 increases to a certain extent, the voltage of a sampling resistance R.sub.1 in series with a sensing element D.sub.1 increases, triggering the base of a transistor Q.sub.2 and causing transistor Q.sub.2 to be in the on state. The emitter of the transistor Q.sub.1. connects with the base of the transistor Q.sub.2, and the on state of transistor Q.sub.2 brings the transistor Q.sub.1 also in an on state. The "on-states" of both transistors Q.sub.1 and Q.sub.2 in turn result in an avalanche cycle to cause the transistor Q.sub.2 to be into a deeply saturated on-state. Thus a very low potential difference will be generated between points A and B. A diode D.sub.2 is provided between points A and C. The potential at the point C connecting with the anode of diode D.sub.2 is higher than that at the point A only by 0.7 volt. Therefore, Potential applied to the base of thyristor D.sub.10 at the point D from the point C through both the adjustable resistance R.sub.10 and the resistance R.sub.11 is so low as to be unable in making the thyristor D.sub.10 on. Therefore, it is impossible to trigger a thyristor TH.sub.1 by the thyristor D.sub.10 connecting with the control grid of the thyristor TH.sub.1. Hence, the lamp L.sub.1 in the operational circuit is locked and is not permitted to switch on again.
However, though the above mentioned protection circuit has the locking function, yet its construction is of the type "once for all". Meanwhile, it has many deficiencies in practice and the protection provided thereby is not reliable. FIG. 3 is a detailed view showing the lamp with the protection circuit shown in FIG. 2. In FIG. 3, the sensor 1 with the sensing element D.sub.1 is attached directly on the reflector 3 of the lamp head. The two points F and G in FIG. 2 can be the welding points formed at the leads of the sensing element D.sub.1 on a printed circuit board (PCB) 6. The two leads have a length about 1000 mm respectively and pass through a main vertical iron tube to the PCB 6. The main vertical tube has three sections, which are connected by threads. In addition, the connection between the vertical main tube and the base of the lamp as well as the connection between the vertical tube and the lamp head are all achieved through threads, which means a plurality of rotations being necessary during mounting of the lamp. The rotations during mounting will twist and are apt to break the wire between point F and the sensing element D.sub.1 as well as the wire between the point G and the sensing element D.sub.1. When any of the two wires is broken, the sensing element D.sub.1 will be disconnected with the circuits of the PCB 6. Thus, regardless of how high a temperature that the sensing element D.sub.1 has sensed, the operation circuit does not work, because the transistors Q.sub.1 and Q.sub.2 in FIG. 2 will not shift to be the on state and the high potential difference is kept between points C, D, which holds the thyristor D.sub.10 to be the on state and in turn holds the thyristor TH.sub.1 also to be the on state in such a manner that the lamp L.sub.1 will be lighted up and will be never extinguished. Therefore, the automatic extinguishment cannot be realized. Moreover, the most serious hidden trouble in such a construction is that the breaking of wires of the sensing element D.sub.1 or a short pass in the element D.sub.1 itself can not be discovered from outside. Therefore, the probability of fire is very great.
In practice, since sensors directly stands on the reflector near the halogen bulb, when a bulb is replaced, sensors will be often touched without intention and the connection between the sensor and electronic circuit may be damaged. The damaged connection will prevent a sensing signal from transmitting to the electronic circuit. Additionally, the members installed on the reflector will mar the reflection.